The recent demonstration that the histone methyltransferase, D0T1L and the acetylysine binding protein BRD4 are required for continued proliferation and survival for subsets of acute myelogenous leukemia (AML) cells points to epigenetic mechanisms as potential therapeutic targets in this disease. Small molecule inhibitors of D0T1L and BRD4 have been developed and show remarkable antiproliferative activity against AML cells providing further rationale for deeper characterization of these processes. The central hypothesis for this project is that small molecule inhibitors of epigenetic mechanisms will effectively target AML cells. We will assess this hypothesis through the use novel small molecules, chemical biological approaches, epigenomic analyses genetically engineered mouse models and genetic screens. In specific Aim 1 we will define the mechanisms by which bromodomains inhibitors suppress Myc and E2F driven gene expression programs. In specific Aim 11 we will define mechanisms of acquired resistance to small molecule bromodomain inhibitors. These studies will inform as to possible mechanisms of clinical resistance to such therapies, and illuminate the cellular pathways through which these molecules suppress proliferation and induce apoptosis. In specific aim 3 we will assess compelling combinations of small molecule inhibitors of epigenetic pathways including the combination of DOTI L inhibitors and BET inhibitors. Given our access to newly developed small molecule inhibitors, the proposed studies have the potential to bring new, more efficacious, less toxic therapies to children and adults diagnosed with AML.